According to conventional motor condition inspection methods and motor characteristic inspecting devices, power is supplied to a motor to drive the motor at a constant rotational speed, and the output of the motor is measured to inspect the characteristics of the motor such as a torque. It is necessary to use a voltmeter, a tachometer, a speed sensor, or the like for inspection in order to perform necessary measurements. Conventionally, it is necessary to remove the motor from the apparatus where the motor is installed and then mount the motor on a dedicated inspecting device in order to inspect the characteristics of the motor, instead of directly inspecting the motor which is installed in the apparatus. Accordingly, it is necessary to remove the motor from the apparatus for each regular check or inspection, which consumes substantial labor and time for the inspection. In addition, the installation condition of the motor cannot be checked by inspecting the motor which has been removed from the apparatus.
For a linear motor, in particular, the installation condition of a mover and a stator (whether a so-called air gap is proper or not) affects the output of the motor. Conventionally, a gap gauge is inserted into a gap formed between the mover and the stator to mechanically measure the size of the gap in order to inspect the installation condition. In this case, however, inspection is performed with the motor removed from the apparatus, and thus a mechanical error may occasionally occur when the motor is reinstalled in the apparatus after the inspection. In addition, it is difficult to inspect whether or not the gap formed between the mover and the stator is totally uniform.
Under these circumstances, the inventors invented a motor condition inspection method and a motor characteristic inspecting device allowing inspection of the characteristics of a motor by computing a counter electromotive force constant based on the frequency value and the amplitude value of the waveform of a counter electromotive force generated when the motor is moved by an external force (Refer to Japanese Patent Application No. 2009-177091).
In the technique disclosed by Japanese Patent Application No. 2009-177091, the frequency is detected based on half the cycle of the counter electromotive voltage (corresponding to an electrical angle of 180°). If abrupt variations (abrupt variations in speed for a linear motor, and abrupt variations in number of revolutions for a rotary motor) are caused in half the cycle of the counter electromotive voltage during acceleration or deceleration, the duty ratio of the frequency before and after a peak value of the voltage may significantly vary, which tends to cause an error in the inspection results. For example, as shown in FIG. 7, the duty ratio (f1A:f1B) of the frequency is significantly varied in a time segment (A), which increases the possibility of an error compared to a time segment (B) in which the duty ratio (f2A:f2B) of the frequency is not significantly varied.